The present invention relates generally to hybrid electric vehicles and, more specifically, to systems for optimizing the operation of hybrid electric vehicles having a connection to an electrical grid.
Hybrid vehicles typically use a combination of consumable fuel (such as gasoline, natural gas, hydrogen, and others) and battery-stored electricity. As hybrids become a major segment of the automobile market, they are displacing electric-only vehicles, as well as conventional vehicles that are powered solely by internal combustion engines or other consumable fuel powered means. The electric power system of an electric-only vehicle is open, in the sense that such a vehicle lacks an onboard means to recharge the battery and therefore must be recharged from an external source. By contrast, the electrical power system of a hybrid vehicle is closed, in the sense that such a vehicle is not recharged from external sources but is instead recharged from an onboard consumable fuel powered means, which may be an internal combustion engine (powered by gasoline, diesel, ethanol, natural gas, hydrogen or another combustible fuel) or which may be a hydrogen fuel cell or other alternative consumable-fuel-based power unit. Passive recharging systems, such as regenerative braking systems, may also be used in hybrid vehicles.
Electric-only vehicles generally employ an open system in which batteries are recharged from an external electric power source, which may be conventional house current, a publicly accessible recharging facility, or any external source of electric power compatible with the vehicle's recharging system. Recharging such an electric-only vehicle from conventional house current alone may limit the useful range of the vehicle to no more than the distance that can be traveled on a single battery charge. External electric power sources for recharging electric-only vehicles could be provided at publicly accessible facilities; however, such facilities have, to date, not become widely available.
Hybrid vehicles employ a closed system in which the vehicle power system incorporates both a battery powered electric motor and a consumable fuel powered means from which the battery may be recharged. Power may be provided to the vehicle drive system by the electric motor and/or the consumable fuel powered means. Hybrid vehicles can refuel using consumable fuels, including but not limited to, fuels which may be available from filling stations, without regard to availability of an external electric power source suitable for recharging. Access to an external electric power source is not required for recharging a hybrid vehicle, because a hybrid vehicle's batteries are recharged from the vehicle's onboard consumable fuel powered means.
Hybrid vehicles have a number of drawbacks including recharging from the vehicle's onboard consumable fuel powered means makes the cost of recharging directly proportional to the cost of consumable fuel. That problem does not present itself with electric-only vehicles, where batteries are recharged from an external electric power source. However, electric-only vehicles may be less practical than hybrid vehicles, since their range is limited when external electric power sources are unavailable for recharging along the route of travel.
The above-discussed problems with electric-only vehicles and with hybrid vehicles are addressed by a third type of vehicle, the plug-in hybrid electric vehicle (PHEV). PHEVs combine the ability of electric-only vehicles to recharge from an external electric power source with the ability of hybrid vehicles to recharge from the onboard consumable fuel powered means. A PHEV has the ability to recharge its batteries either from a source outside the vehicle (such as by way of an electric plug) or from an onboard means such a consumable fuel powered means.
PHEVs are complementary with the electric power grid as systems for managing energy and power. Recent research has suggested that there is economic benefit for the utilities, for the drivers (who are also electric grid users), and for society as a whole in using the PHEV as an extension of the grid, both as a power source and a power reservoir, a so-called Vehicle-to-Grid (V2G). The power grid has essentially no storage (other than its 2.2% capacity in pumped storage), so generation and transmission must be continuously managed to match fluctuating customer load. This is now accomplished primarily by turning large generators on and off, or by ramping them up and down, some on a minute-by-minute basis. In contrast, plug-in hybrid electric vehicles, in the aggregate, have a large amount of electrical storage capacity.
The high capital cost of large generators motivates high use (average 57% capacity factor). In contrast, most vehicles are designed to have large and frequent power fluctuations, since that is in the nature of roadway driving. Personal vehicles are cheap per unit of power and are utilized only 4% of the time for transportation, making them potentially available the remaining 96% of time for a secondary function. Thus, a bidirectional coupling of the hybrid vehicle to the grid with V2G could achieve benefits for both the electric power grid as well as the PHEV fleet. In particular, this may be accomplished by using the PHEV as an extension of the grid, both as a power source and as a power reservoir.
From the perspective of the hybrid vehicle fleet, grid coupling enables a lower energy cost, since, while charging, the cost of energy from the grid is normally less than the cost of energy from fuel in the vehicle. Also, the PHEV owner may receive monetary compensation by utility companies for the power fed back into the grid. Another benefit is a reduction in environmental pollution, since electric energy production is relatively environmentally friendly as compared to vehicles powered by internal combustion engines.
From the perspective of the grid, the fleet of PHEVs can act as a controllable load to smooth grid load. That is, by injecting electrical energy into the grid, the PHEV can be used as a reserve power unit to off set the loss of a power plant, as replacement for peak power units, as part of a micro grid or as a stand alone generator. During non-peak periods, the PHEV can be used by the grid for electrical storage. Both of these uses in tandem allow the utilities to load-balance demand and supply so as to better manage overall grid capabilities and utilization. This, in turn, reduces the requirements on the utilities to build power generation facilities to cope with peak demand. In a V2G system, the utilities would reimburse or otherwise provide an economic benefit to the driver for the use of the traction battery in the vehicle.
However, the current vision of V2G does not coordinate the numerous parameters necessary in order to optimize either the driver's direct economic benefit or the grid's direct utility function from the use of the traction battery or any other economic or social benefit. These parameters may include, for example, the state of the vehicle batteries at the time the vehicle is plugged into the grid, the cost of fuel relative to the cost of energy from the electric power grid, the driver's needs as various times, etc.
The complexity of addressing such problems is increased when one considers a broad definition of the notion of “benefit” for the driver, the grid, and society. For example, the driver's benefits could be financial—how much does the driver save on costs or even get reimbursement from the utilities for the V2G use of the vehicle. However, many drivers also value their “green benefit”. Utilizing V2G techniques may enable drivers to reduce their carbon footprint or to obtain or trade carbon footprint credits.
The complexity of optimizing V2G systems is further increased by the fact that, in some embodiments, solutions change as the vehicle changes its position relative to available external electric power sources, which is something a vehicle necessarily does when it is put to its intended use of moving from place to place. Furthermore, to be viable, V2G systems must be especially cost-effective for the driver in order to engage his/her participation in the process.
As can be seen, there is a need for a way to optimize the operation of V2G PHEVs to maximize the benefits for both the driver, the utility companies operating the grid, and society as a whole. There is also a need to optimize a V2G system which takes into account the numerous relevant factors such as the state of the vehicle's batteries at the time it is plugged into the grid, the needs of the grid as any particular time, driving habits of the vehicle owner, carbon footprint, and others.